Continuous Renal Replacement Therapies (CRRT) involve the following procedures:
1. CVVH (Continuous Veno-venous Hemofiltration) is the most frequently used method for treating acute kidney failure. The uremic toxins and ultrafiltrate are removed by means of a hemofilter (convective clearance). To remove uremic toxins in sufficiently high concentrations during treatment, relatively large quantities of ultrafiltrate must be withdrawn and subsequently added to the blood again by the hemofiltration solution either after the filter (post-dilution) or before it (pre-dilution).
2. During CVVHD (Continuous Veno-venous Hemodialysis), the patient's blood is dialysed in a capillary filter (dialyser) against a dialysis solution (counter current method). The uremic toxins diffuse out of the blood inside the capillary into the dialysis solution flowing outside the hollow fibre (diffusive clearance).
3. CVVHDF (Continuous Veno-venous Hemodiafiltration) is a combination of CVVH and CVVHD. It makes use of CVVH's convective clearance as well as CVVHD's diffusive clearance.
4. CVVHFD (Continuous Veno-venous High-flux Dialysis) also combines CVVH with CVVHD, but involves substitution inside the hemofilter (internal substitution). This method requires just three pumps instead of four as in the case of CVVHDF. The system is identical in design to CVVHD.
5. SCUF (slow, continuous ultrafiltration) is used to gradually remove excess body water from patients suffering from hyperhydration. The blood is routed via a capillary filter with a highly permeable membrane (hemofilter), excess volumes being removed at low flow rates (ultrafiltration). Not really a dialysis technique, this procedure is used for volumetric relief in the case of diuretic-resistant hyperhydration especially for patients with cardiac problems.
Besides the CRRT techniques, it is also possible to use intermittent techniques which, as in the case of chronic dialysis, are only applied for limited periods interspersed by dialysis-free intervals.
In addition to these extracorporeal therapies, in which the blood is treated outside of the body, peritoneal dialysis (PD) may also be used as an intracorporeal therapy. In this case, the blood is cleaned by means of a special liquid (PD solution) in the peritoneal space the peritoneum serving as the dialyser in this case. Peritoneal dialysis is especially suitable for children, but also used for patients with unstable circulation or a high risk of hemorrhage.